Although there are many ways of measuring blood pressure in rats, a non-invasive method which can be used without preheating or anesthesia, and can measure diastolic as well as systolic pressure, is badly needed. The present application proposes to examine photoelectric and oscillometric sensors for detecting end-points for systolic and diastolic pressures indirectly in unanesthetized rats. Because tail-cuff methods require preheating to dilate caudal vessels, the feasibility of indirect measurement from a hindleg will be explored. Any indirect method that is finally developed will be validated by comparison with phasic aortic pressure recorded simultaneously from indwelling catheters in trained awake normotensive and hypertensive rats. Its ability to determine drug-induced changes in systemic pressure will likewise be tested following intravenous administration of pressor drugs like angiotensin and norepinephrine, or of hypotensive ones like phentolamine or pentolinium. Similarly, its adaptability for chronic measurements during developmnt of hypertension in young rats or during chronic antihypertensive treatment in aging hypertensive ones will also be explored. Because hypertension is currently a major health hazard in the United States and much of hypertension research is done on rats, a method that allows accurate measurement of blood pressure during a significant portion of the rat's lifespan is absolutely essential. If a good non-invasive method can be developed it would facilitate research in experimental hypertension and thus improve our understanding of the disease.